Campbell Scientific CS110 Electric Field Meter - Manual (Page 27)

CS110 Electric Field Meter
covering the stator with a clean Zero Electric Field Cover (PN: 17642). Fair
weather field site correction is not recommended for lightning warning
applications because of the relatively poor accuracy in determining Csite.
6. Lightning Warning
Lightning warning devices fall into two classes: lightning detectors and electric
field monitors. Stand-alone lightning detectors provide warning based on
nearby discharges, but give no warning until a detectable discharge occurs.
Electric field monitors measure the atmospheric electric field, indicating the
presence of nearby electrified clouds capable of producing lightning
discharges. Consequently, electric field monitors can give warning at the
beginning of storms prior to hazardous discharges. Both lightning detectors
and electric field monitors are employed in high-risk applications.
Lightning safety guidelines based on human observations exist and should
not be ignored simply because of the presence of sensitive electronic
instrumentation. The NOAA 30/30 rule suggests seeking shelter if thunder is
heard within 30 seconds of a lightning flash (approximately 6 miles), and
remaining in a sheltered area for 30 minutes after the last lightning or thunder
before resuming outdoor activities [NOAA].
It should be noted that no method of lightning warning completely
eliminates the risks associated with lightning. As mentioned, lightning
detectors give no warning until a detectable discharge has occurred.
Atmospheric electric field yields warning prior to the “first strike” for storms
developing overhead, along with some indication of the end of a thunderstorm.
Yet there are occurrences of cloud-to-ground lightning discharges striking the
ground several miles away from the electrified cloud where the discharge
initiated [NOAA]. Electric field monitors may give no practical warning in
these instances because the electric field in the vicinity of the strike point may
not indicate hazardous levels until milliseconds before the strike.
Consequently, while lightning warning systems can greatly reduce the
probability of death or injury from lightning discharges, they cannot
reduce this probability to zero.
19